The creation of a biohybrid robot, a living machine that combines mechanical components with organic elements, might sound like something straight out of a science fiction story, but in fact, it’s been the subject of scientific experiments for years. However, while previous groups of researchers have tended to stick with conventional sources of organic material, like muscle tissue from mice or rats, a team of bioengineers at Case Western Reserve University (CWRU) opted for a more unusual source in constructing their recently revealed biohybrid creation: the sea slug.
What is the CWRU biohybrid robot all about?
The CWRU biohybrid robot is a unique combination of flexible 3-D printed components and tissue from Aplysia californica, a type of sea slug also known as the California sea hare. 3-D-printed polymers make up the basic structure, or skeleton, of the robot, which consists of two arms and a body: in appearance, it’s somewhat similar to a tiny lobster. The next step for researchers was to extract the sea slug’s I2 muscle (a Y-shaped muscle from the mouth area) and attach it to the robot’s polymer skeleton. While the team originally tried working with muscle cells, they found that using the whole I2 muscle was more far more effective because its shape was a natural fit for the shape of the robot.
This I2 muscle is what ultimately allows the robot to move around. When the muscle contracts, as it does when external electrical current is applied, the robot can use its arms to push or drag itself forward. This style of locomotion is similar to that of sea turtles, which the research team used as a movement model when developing the robot. While the robot is able to make noticeable progress, it’s certainly not going anywhere quickly just yet: its current speed is just over 0.4 centimeters per minute. Furthermore, while its movements can be turned on or off by the application of electrical current, it’s not yet possible to steer or direct the robot.
Why the sea slug?
Though the sea slug might seem like an unusual selection for the “bio” part of a biohybrid robot, it was an ideal choice for the CWRU team thanks to one major quality: its durability. The sea slug lives in areas of the Pacific Ocean where shifting tides mean that its environments alternate between deep water and shallow pools, both of which can vary significantly in terms of temperature, salinity, and other factors. This high level of environmental variation means the sea slug has developed into an extremely durable organism right down to the cellular level, thus making it a good choice for a robust and versatile robot that can function effectively under a range of different conditions. The mammal or bird muscles that researchers have previously used in biohybrid robot experiments, on the other hand, require much more strictly controlled environments in order to operate properly.
In addition, sea slug cells and neurons have the advantage of being big and, therefore, easier to work with.
What could the CWRU biohybrid robot be used for?
Robots like the CWRU biohybrid robot could be ideal candidates for searching and exploration tasks in environments that are inaccessible to humans or conventional robots. Deep-sea exploration has been cited as one area where teams of biohybrid robots could play an important role; for example, they could search for the source of toxic leaks or oil spills underwater or scour the ocean floor for crucial debris from airplane crashes or shipwrecks.
What’s the next step for researchers?
There is still a long way to go before we can expect to see biohybrid robots swimming around on their own. At present, the CWRU research team is focusing on improving muscle control and direction in the robots by using the sea slug’s own ganglia, which are bundles of nerve cells that transmit signals to the sea slug’s I2 muscle during feeding. Using these ganglia as an organic way to control movement allows for much more complex maneuvers compared to those generated by human control. Furthermore, ganglia also have the ability to “learn,” which means that the robot could eventually be trained to move both forward and backward in response to different signals.
Another major goal of the research team is to make the robot completely organic. The team is experimenting with using collagen from the slug’s skin to build an alternative scaffold (rather than one made from polymers), which would be both lightweight and strong. The major advantage of a completely organic robot would be that, if robots were unable to be recovered from remote land or ocean areas after they were released, they would simply decompose naturally rather than polluting the location with battery chemicals and metals.